Hi there,

I know three big ones in the Zürich area:

Wehrli (I found some items overpriced but has a good assortment)

Baby World

Probaby

For maternity clothes H&M as Sutter said is your best bet (and much cheaper too), otherwise try the online (search for Umstandsmode).

Prepare yourself to be disapointed because of lack of assortment

HTH